Controllers of the aforementioned type are required in satellites in order to reduce the angle of deviation of the attitude of the satellite from a reference direction to a permissible degree which may result from a number of individual criteria. This deviation may significantly lessen or even completely eliminate the usefulness of the satellite in its path.
U.S. Pat. No. 3,984,071 describes an attitude stabilization apparatus for a nutating satellite, wherein a sensor generates an error signal and the error signal is supplied to a filter. After the filter, a summing point is arranged, from which the signal is supplied to two Schmitt triggers. The first Schmitt trigger is activated when the signal from the sensor indicates a positive error of a certain magnitude; the second Schmitt trigger is activated when a negative error is present. An output of each Schmitt trigger leads to a multivibrator which delivers a pulse as soon as it is triggered. The other output of each Schmitt trigger leads to an OR element which is also connected to the output of the multivibrator. The output of the OR element is directed to another OR element, the output of the latter activating a first nozzle for generating a counter-torque against the positive angle error. The essence of the invention lies in the fact that, after the first-mentioned OR element, a counter is arranged which is set to zero by each pulse delivered by the OR element and starts a count which is compared to the normal duration of a nutation. If, since the last time the counter has been set to zero, a certain portion of a nutation period has elapsed, preferably 5/8 of such a period, without a new pulse having been delivered by the first OR element, then this counter activates (through the already mentioned second OR element) the thrust nozzle for another ignition.
In this manner, the satellite is to be prevented from swinging back and forth between the boundaries of a predetermined band caused by the attitude control which would result in a high fuel consumption and, therefore, would reduce the service life of the satellite in its path, or the possible payload.
However, it is a disadvantage in this apparatus that not every variation of the parameters, for example, the moment of inertia or the rate of rotation of the reaction wheel which must lead to a change of the nutation period, is recognized.
It is an object of the present invention to specify an apparatus for an active control which provides attitude stabilization independently of the parameter variations.